Plastics coated metal tube of the type whose manufacture is described in European Pat. No. 0024220 consists of a thin walled tube of aluminium or aluminium alloy coated both internally and externally with a layer of a thermoplastic material, for example polyethylene. The tube is generally manufactured by forming a continuous strip of aluminium or aluminium alloy into a U-shape, transforming the U-shape into an overlapping tube, welding the overlapping edges together and immediately extruding polyethylene onto the interior and exterior surfaces of the tube, if necessary together with an intermediate adhesive layer to promote adhesion of the polythylene to the metal tube. The aluminium or aluminium alloy is generally approximately 0.2 mm thick and the inner and outer plastics coatings are generally each of the order of 1 mm thick.
Such plastics coated tube is rapidly replacing the more traditional copper pipe in the domestic and industrial plumbing fields in view of its lower production cost, greater ability to be produced, stored, transported and used on site in virtually continuous lengths. Such plastics coated metal tube does, however, need to be coupled to fixed appliances and various plumbing fittings, and conventional compression joints and fittings of both the manipulative and nonmanipulative type may be used for this purpose.
Plumbing fittings of this nature are traditionally manufactured from brass because of its durability. However, it has been found that the use of brass fittings in association with the plastics coated aluminium or aluminium alloy tube can result in problems of anodic corrosion in those instances where the aluminium or aluminium alloy in the tube comes into contact with the brass fitting. When the corrosion becomes severe, leakage can occur and this can be totally disastrous for a large scale pressurized piping system.
The present invention seeks to provide connectors for plastics coated metal tube of the type described above, in which contact between the connector and the metal of the tube is prevented.